Anywhere between 40 and 70 percent of food products sold in California grocery stores contain some genetically engineered ingredients.

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Voters on Tuesday were on track to reject Proposition 37, which would have made California the first state in the nation to require manufacturers to label all foods with genetically-modified ingredients.

With more than 50 percent of precincts reporting, about 55 percent of voters opposed the measure, and just 45 percent supported it.

Opposition to the potential law was heavily bankrolled by chemical companies and food manufacturers. And the majority of that funding – some 93 percent of the $44 million raised to defeat the proposition – came from out of state.

By comparison, the Yes on 37 camp poured some $7 million into a campaign dubbed the "crusade against Frankenfood."

Genetic engineering involves manipulating the genes of an organism, usually with the goal of improving a plant’s resistance to pests or to allow a plant to withstand the use of pesticides.

While there have been no long-term studies that suggest consuming genetically-modified foods are harmful to humans, supporters of Prop. 37 cited a lack of evidence to the contrary in their arguments for the measure.

"Whether you buy genetically engineered food or not, you have a right to know what you are buying and not gamble on your family’s health," supporters said.

Opponents of the measure claimed they would be buried by the extra costs of printing new labels, and would have to pass that cost on to consumers.

It’s estimated state enforcement of the proposition would cost taxpayers between a few hundred thousand dollars to more than $1 million annually, according to the Legislative Analyst’s Office (LAO).

As it’s written, Prop. 37 contains a number of exemptions, including foods made entirely from animals and certified organic food. Wine, which makes up a huge industry in California, would also be exempt from the proposed food-labeling law.

Other exemptions include foods that are:

certified organic;

unintentionally produced with genetically engineered material;

made from animals fed or injected with genetically engineered ingredients;

processed with or containing only small amounts of genetically engineered ingredients;

administered for treatment of medical conditions;

sold for immediate consumption, such as in a restaurant;

alcoholic beverages.

Experts reiterated throughout the campaign season that California’s decision whether to label genetically-modified foods could have national consequences.

“California could lead the nation in this,” said Bob Stern, a California campaign finance expert, told NBC4 earlier this month. “If it passes, it spreads. If it fails, it may be dead.”

In 2011, 88 percent of all corn and 94 percent of all soybeans produced in the U.S. were grown from genetically-engineered seeds, according to the non-partisan Legislative Analyst's Office.

Some of the most common genetically-engineered crops include alfalfa, canola, cotton, papaya, sugar beets, and zucchini. And are used to make food ingredients, such as high fructose corn syrup.

The LAO claims anywhere between 40 and 70 percent of food products sold in California grocery stores contain some genetically engineered ingredients.